Electrical pressure connector



May 24, 1960 H. H. KOBRYNER EIAL 2,9385191 ELECTRICAL PRESSURE-CONNECTORFiled Feb. 24, 1958 mmvroxs l-lfAMAN H. K051? YNEIE y GL'ORGE A. OLSENAT ORNEY space is available.

United Patent ELECTRICAL PRESSURE CONNECTOR Herman H. Kobryner, ForestHills, and George A.'0lsen,

Farmingdale, N.Y., assignors to Murray Manufacturing Corporation,Brooklyn, NY.

Filed Feb. 24, I958, Ser. No. 717,114

2 Claims. (Cl. 339-272) This invention relates to pressure connectorsforelectrical conductors, and more particularly to such connectors suitablefor a wide range of wires; for example, wires from number 4 (A.W.G. B. &S. gauge) to 250 MCM. jv Electrcial pressure connectors are now wellknown in the industry. Generally, the connector comprises a cradlemember in the shape of a U for supporting a conductor, a bridge memberextending across the open end of the U, and a pressure applying meansmounted to the bridge member. The-cradle member is usually formed withslots in the opposite legs thereof, adjacent the base, for accommodatinga fitting which, for example, may be a bus bar. The pressure applyingmeans, in connectors of the size to which this invention relates, isusually a pressure plate swivel-mounted at an end of a screw. Thepurpose of the pressure applying means is to force the conductor againstthe fitting and to maintain such contact for a substantial period oftime.

Although the connector is comparatively simple in construction,considerable etfort has been expended by the industry for thedevelopment of a standardized connector which is suitable for a widerange of wires; from relatively small, e.g. No. 4, to relatively large,e.g. 250 MCM.

A standardized connector must fulfill many varied and diverserequirements. For example, the connector should be capable of retainingconductors of either aluminum or copper with equal efficacy. When it isrealized that aluminum cold-flows under high pressure, the fulfillmentof this requirement is not a trivial consideration. If such pressure isapplied as to cause the aluminum to cold-flow, the etfective holdingpower of the connector is decreased, and if the conductor is subjectedto vibratory forces, it will become detached from the connector.Therefore, the force exerted by the pressure applying means must besufficient to press and maintain the conductor securely against thefitting without causing the aluminum to cold-flow.

Another problem is the selection of the proper type of screw for drivingthe pressure plate. In most of the known type connectors, the type ofscrew is determined by the size of the connector, and the size of theconnector is controlled by the size of wire for which it is intended.The smaller connectors generally use a screw having a slot for a screwdriver, and the larger connectors use a screw having a head adapted fortightening with a wrench. Tests have shown that technicians using ascrew driver exert a torque of approximately 50 pounds-inch, whereaswhen using a wrench, they exert approximately 250 pounds-inch.Therefore, connectors using wrench-head screws must be considerably morerugged to withstand this additional force. This ruggedness addsundesirably to the bulk of the connector which limits its usefulness todevices where sufiicient It would seem, therefore, advantageous to usethe slot type screw; however, such screw does not permit sufiicientforce to be exerted to hold securely the larger size conductors. TheUnderwriter Standards require that a connector designed for Wire up to250 MCM be capable of withstanding a wiggle test with a 60 pound load atthe end of the wire and a pullout test with a 500 pound load. Further,the connector must be able to carry '250 amperes without overheating.That is, the temperature rise of the connector may not exceed 25 C.,while the connection conducts the rated current.

The temperature rise is a function of several factors, a few of thesebeing the area of contact between the conductor and the fitting, theforce of contact, and the heat produced by eddy currents and hysteresislosses in the connector body. The area and force of contact aredetermined largely by the design of the connector, and the hysteresisand eddy current losses are a result of the magnetic fields traversingthe connector body.

Another problem in developing a standardized connector for a wide rangeof wires is the design of a cradle member which is capable of centeringthe Wires (small and large), on the fitting.

Thus, because of these many varied problems requiring solutions whichappear to conflict with each other when combined in a unitary structure,manufacturers have in the past designed connectors for the specificjobs.

Thus, it is a primary object of my invention to provide a standardizedconnector capable of accommodating a wide range of wires of eitheraluminum or copper.

It is a feature of my invention to provide a connector utilizing a screwadapted to be tightened by a screw driver rather than a wrench, wherebythe connector is subjected to the smaller forces, thereby permitting theconnector to be. made smaller in size.

It is a further feature of my invention to provide a. uniquely shapedscrew, in combination with the connector, which exerts a greater forcethan is exerted by the conventionally designed screw.

It is a further object of my invention to provide a cradle membercapable of centering the wide range of wires on the fitting.

It is another object of my invention to reduce the eddy current andhysteresis losses in the connector.

In accordance with a first aspect of my invention, the connectorcomprises a cradle member in the shape of a U, the opposite legs thereofhaving slots extending along the base and conforming to the shape of afitting. The fitting is positioned through the slots and a conductor ismounted between the legs of the U on the fitting. A bridge member issecured to the opposite legs of the cradle member, and means areprovided mounted to the bridge member for pressing the conductor againstthe fitting. This aspect of my invention is characterized by making thecradle member of non-magnetic material whereby the eddy current andhysteresis losses in the connector are reduced.

In accordance with another aspect of my invention, the cradle membercomprises a pair of projections on the inside of each leg, theprojections being of similar size and shape, and extending upwardly fromthe slots. The projections increase gradually in size towards the slots,whereby for a relatively small conductor the projections tend to centerthe conductor on the fitting, and for a relatively large conductor theprojections impress themselves into the sides of the conductor when theconductor is pressed against the fitting, thereby anchoring theconductor to the connector.

In accordance with still another aspect of my invention, the pressureapplying means comprises a screw of the type adapted to be tightened bya screw driver, and a pressure plate swivel-mounted to an end of thescrew. This aspectof my invention is characterized in that the end ofthe screw bearing against the pressure plate is tapered inwardly,thereby correspondingly increasing the force resulting from the torqueapplied to the screw.

The above-mentioned and other featuresand objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction withtheaccompanying drawings, wherein:

Fig. l is a perspective view of my novel connector; and

Fig. 2 is an exploded view of the connector.

Referring now to the figures, the connector comprises a cradle member 1made of non-magnetic material, preferably a copper alloy such as bronze.The cradle member is in the shape of a U having a pair of legs 2, 3attached to a base 4. The legs 2, 3 are of unequal lengths, the leg 2.being shorter and terminating in a lug 5 extending substantially atright angles to the leg and away from the other leg. The longer leg 3 isprovided with a slot 6 towards the free end thereof, a given distanceabove the lug 5.

The opposite legs 2, 3 are formed with slots 7, 8 respectively,extending along the base 4 and conforming in shape to an electricalfitting 9. As shown the slots 7, 8 are aligned and located intermediatethe vertical edges of the legs.

The top of the cradle member is enclosed by an angleshaped bridge member10 comprising a first portion 11 extending across the open end of thecradle member and terminating in a lug '12, adapted to fit into the slot6 in the leg 3. A second 'poition 13 of the bridge member 10 is bentsubstantially at right-angles to the first portion 11 and overlaps asmall part of the upper-portion of the shorter leg 2; the lug 5 fittinginto a slot 14 in the portion 13.

-A pressure applying means for pressing a conductor 15 against thefitting 9 when the fitting and conductor are positioned in the cradle issecurely mounted to the bridge member 10; The pressure applying meanscomprises a screw 16 of the slot type and a pressure plate 17swivel-mounted to an end of the screw. The screw 16 is threaded into atapped hole 18 centrally located in the portion 11 of the bridge member.The pressure plate 17 is formed with a cup-shaped recess in the bearingsurface, with a hole in theccnter thereof. The end of the screw 16 isnarrowed into the shape of a pin and riveted over the periphery of thehole. The depth of the recess is selected to provide clearance betweenthe end of the riveted part of the screw and the conductor, therebypreventing damage to the conductor.

The pressure plate 17 is formed in the shape of an inverted V whichshape tends to center the conductor therein and centrally on thefitting. The bearing surface of the pressure plate is knurled so thatwhen the pressure plate forcesthe conductor against the fitting,theknurled surface is impressed into the conductor, thereby increasingthe holding power of the connector. Further, as a result of the V-shapedpressure plate the contacting area between the plate and .the conductoris increased in that two surfaces of the plate act against the conductortending to center it on the fitting.

One of the attributes of my invention is that it is relatively small forthe wide range of wires which it is capable of accommodating. Itsrelatively small size is pos sible because I use a screw of the typeadapted to be tightened by a screw driver rather than by a wrench. Aspreviously mentioned, a technician using a screw driver exerts a torqueof approximately 50 pounds-inch whereas a technician using a wrenchexerts a torque of about 250 pounds-inch. Thus, by using a slot-typescrew a structure only as strong is required which is far less bulky,and capable of use in devices where space is a controlling factor.

However, inorder to obtain the'necessary force for merely to attach thepressure plate to an end of the screw. It is important that the screw beshaped to increase the force applied to the pressure plate.

The force exerted by the screw is proportional to the torque applied andinversely proportional to the diameter of the screw. That is: F=T/R. Theforce F is that force applied by the pressure plate on the conductor.This force is equal to the sum of the torques required to overcome thefrictional force where the screw threads engagethe bridge member dividedby the radius of the screw, and the frictional force between the end ofthe screw and the pressure plate divided by the radius of the bearingend of the screw. Therefore, with given materials, and applied'torque,the force applied by the pressure plate varie inversely with the sum ofthe above mentioned radii. Thus, in order to obtain the desired forcethe end of the screw bearing against the pressure plate is tapered asshown at 19.

To improve further the holding power of the connector for large sizewires, or alternatively to guide the smaller size wires centrallybetween the legs of the cradle, projections 20 are provided on each ofthe legs 2, 3. The

- projections are of similar shape and size and are located at theopposite ends of the respective slots.

The projections 20 are pyramidal in shape; the base of the pyramidscoinciding'with the upper edge of the slots and gradually decreasing insize as they extend upwardly. The connector parts are dimensioned sothat the pressure plate fits with slight clearance between theprojections, whereby when the larger size wires are forced against thefitting the projections'impress themselves into the sides of theconductor, thereby anchoring the conductor to the connector. The smallersize wires are guided centrally between the legs by the projections andin a position to'be guided further by the V-shaped pressure plateintothe angle of the V and against the fitting.

The dimensions of the projections are selected so that the distancebetween the apices at the base of the pyramids is less than the width ofthe fitting. Thus, as shown in dashed lines in Fig. 1, the fitting mayalternatively be inserted between the legs of the cradle member.

While I have described above the principles of my invention inconnection with specific apparatus, it is to be clearly understood thatthis description is rnade only by way of example and not as a limitationto the scope of my invention as set forth in the objects thereof and inthe accompanying claims.

What is claimed is:

l. A pressure connector for connecting an electrical conductor to afitting, comprising a cradle member in the shape of a U, one leg of theU being longer than the other leg, the shorter leg being terminated in alug extending substantially at right-angles to the leg in a directionaway from the other leg, the opposite legs having slots extending alongthe base and conforming to the shape of the fitting,whereby the fittingmay be securely mounted to said connector through said slots, an angleshaped bridge member having a first portion extending across the openend of the U and terminating in a lug fitting into a slot in said longerleg of the U, a second portion of said angle shaped bridge memberoverlapping said shorter leg and having a slot for accommodating the lugextending from said shorter leg, whereby the bridge member is secured tosaid cradle member, a screw adapted to be tightened by a screw drivermounted'in said first portion of said bridge member, a swivel-mountedpressure plate connected to an end of said screw, the end of said screwbearing against said pressure plate being tapered radially inwardlywhereby the force result- .ing from the torque applied to the screw iscorrespondingly'increased, said pressure plate being shaped to centerthe conductor centrally on the fitting, said cradle .memberdncluding apair of projections on the inside of .each of said legs,;the projectionsbeing of similar size and shape, each pair being located directly abovethe respective slots and extending a given distance towards thecorresponding projections of the other pair, the projections beingshaped to gradually increase in size towards the respective slots,whereby for a relatively small conductor the projections tend to centerthe conductor on the fitting and for a relatively large conductor theprojections impress themselves into the opposite sides of the conductorwhen the conductor is pressed thereagainst, thereby anchoring theconductor to the connector.

-2. The connector according to claim 1, wherein said cradle member ismade of non-magnetic material, and the for gripping the conductor.

References Cited in the file of this patent UNITED STATES PATENTS2,117,112 Buchanan May 10, 1938 2,132,967 Pennell Oct. 11, 19382,198,262 Bergan h- Apr. 23, 1940 2,539,628 Kingdon Jan. 30, 19512,746,025 Radack May 15, 1956 2,780,793 Gambale Feb. 5, 1957

